It’s finally time for Homer Simpson and Peter Griffin to bro down and drink up. On Sept. 28, from 9 p.m. all the way to 10 p.m., the animated worlds of Fox’s The Simpsons and Family Guy will collide colossally when Family Guy’s season premiere features the Griffins breaking bread/donuts with the Simpsons. Friendships are formed between the two families before Homer and Peter get in a massive fight over their respective beer of choice.

Dying to know how this crossover came to life? Wondering what to expect when the Quahog crew cruises over to Springfield? Still trying to free up some DVR space by powering through the leftovers of the FXX’s Simpsons marathon? You’re on your own on that last one, but Family Guy co-showrunner/executive producer Richard Appel gave EW some insight and intel into the long-awaited mashup.

1. Family Guy received permission from The Simpsons to borrow Springfield for an episode… just as long as it took good care of the place. Certainly in Family Guy’s favor was that the person doing the asking, Appel, was more than just a fan of The Simpsons—he was a writer-producer on the show for four seasons. In short, Simpsons creator Matt Groening and executive producers James L. Brooks and Al Jean knew at least that Homer and his family were in responsible and knowledgeable hands. “From the start, Al and Jim and Matt were on board with it being an episode of Family Guy… with the condition ‘Do us proud, please don’t kill Marge, and let us read the script,” says Appel. “But there was a welcomed level of trust on both sides that they weren’t going to rip the script to shreds and we weren’t going to rip Springfield to shreds…. We said to Jim and Al and Matt: ‘It’s not our idea to do something that you’d be watching for the first time when it airs and say: What have we done? We want it to be something you’ll also like.’”

That did require a moment of reassurance, though. The script for “The Simpsons Guy,” written by Family Guy co-executive producer Pat Meighan, is self-effacing and self-aware, winking at criticism that Family Guy is a rip-off of The Simpsons but also that The Simpsons is past its prime. “Peter Griffin takes a few shots at The Simpsons, and Jim was like ‘Oh, is that necessary?’” recalls Appel. “And I said ‘Jim…’ And as soon as I just said ‘Jim…,’ he was like “No, you’re right, you’re right! My God, you take so many shots at yourself, Peter has to give back. And I said, “Thank you.’” The Simpsons producers were invited to attend the table read for the episode and give notes, but “to their credit, they only had two lines that they noted,” says Appel. One of them involved a line by Hans Moleman, who runs Peter down with Peter’s car. “When he gets out of the car, originally it was something like, ‘Just like the Farmers Market all over again,’” says Appel. “And Matt called to say, ‘He’s such a loveable guy. Do we have to now establish as his history that he mowed down innocent people at a farmer’s market?’ And I said, ‘That’s a pretty mild request.’ So we changed that.”

2. There was a reason that Family Guy didn’t make a crossover earlier in the show’s run. And it wasn’t because of the rivalry between the shows, which folks on both sides describe as healthy and friendly—even though they have taken swipes at each other over the years. (“I’ve worked with Matt and Jim and Al and [Family Guy creator] Seth [MacFarlane], and I know that they’re all fans of one another,” Appel says. “And I know that when Family Guy came on the air, the person who was happiest was Matt because he thought it was great for animation.”) Rather, the producers felt that TV watchers needed an accumulated knowledge of Family Guy’s world and tone to appreciate the differences between the two series and to have their expectations for a crossover episode “met and upended,” says Appel. “You have to have a pretty strong familiarity with both shows to think, ‘Now let’s see what happens when they mix.’ It’s a rare thing that any show is on the air for 15 years, much less 25, where you get to play with that.”

3. When the actors from both shows gathered to read through the script for the first time, the vibe was… “Electric” is the word used by Appel, who notes that the packed room burst out in spontaneous applause when Dan Castellaneta, who voices Homer, delivered his first line. There was one problem, though. “After the table read, I did say to Seth, ‘We’re six minutes long,’” Appel says with a chuckle. “And he said, ‘Um, I would not worry about the length. Fox will be happy making this an hour long.”

4. Family Guy’s writers spent considerable time finding fun(ny) ways for the characters to pair up. Our two overweight, immature, no-shame patriarchs, Peter and Homer, are the must-see matchup. And the second-biggest story in the episode involves Stewie skateboarding and making prank calls with his new idol, Bart. “The idea of Stewie being charmed and enamored of Bart’s, almost comparatively speaking, Huck Finn rakishness and rascaliness, in contrast to Stewie and what he has has done on Family Guy over the years, presented itself pretty quickly,” says Appel. (The episode also toys with signature characteristics of both shows, such as finding a way for Stewie to utter Bart’s catchphrase “Eat my shorts.”) Meanwhile, Meg will get some much-needed lessons in self-confidence from Lisa, and Marge and Lois will do some mom-bonding. Later in the brainstorming process of the episode, MacFarlane pitched an idea to give Brian and Santa’s Little Helper a joint story. “Seth always loved the difference between those two dogs,” says Appel. “Those characters could not be more different. Brian is this writer, would‑be intellectual, if anything overthinker and Santa’s Little Helper, as Brian says, speaks a ‘gutter language.’ He just barks.” (Chris was also worked into Brian-Santa’s Little Helper plot.)

How many of your favorite Springfield residents will make an appearance? There are 25 speaking parts for Springfieldians, and dozens more are briefly seen during a twist later in the episode that brings “similar” residents from both towns together. “You can’t get around the fact that both worlds have an anchorman and both worlds have a sea captain,” says Appel, adding: “Consuela and Bumblebee Man don’t really have that much in common, but we knew that seeing them together would get a laugh.” The Family Guy writers printed out a list of the hundreds of Simpsons characters to remind themselves of their myriad options. “It was kind of like being at a great hotel Sunday brunch where you just walk down the line and think, ‘Sure, I’ll have a little Dr. Nick and Patty and Selma. Yes, I’ll take two Sideshow Mel’s,’” says Appel. “But that was kind of the fun—after the story is all there, you can go back and start [adding in] things not just for the fans, but for us. We’d like to see them too.”

5. Among the many targets of this crossover episode? Crossover episodes. “The Simpsons Guy” winks at the stigma of crossover episodes being forced, ratings-grabbing gimmicks, with a little help from guest star Julie Bowen. “We hope it will be a very satisfying experience for the true fans, who probably if they’re true fans, will approach the episode skeptically,” says Appel. “And we acknowledge that at the top of the show, where the history of crossover episodes on network TV isn’t necessarily a glorious one. We’re inviting them from the start, at our own peril, to hold us to pretty high standards and say, ‘Was it worth it? Does this feel like a stunt or did this feel like a satisfying, once-only melding of these two worlds?’ As long as it’s 51 percent who like it, that’s fine.”

6. At first, the Griffins and the Simpsons didn’t see eye to eye. To ensure a seamless, visually pleasing fusion of the two shows, Family Guy supervising director Peter Shin—who had previously worked as a Simpsons layout artist—made a few adjustments to Peter & Co. for their Springfield visit. ”We had to dim our whites on the Griffins’ eyeballs so they didn’t jump out and [look] too bright compared to the Simpsons,’” he notes. (Also, longtime Simpsons supervising director David Silverman dropped by the Family Guy offices to conduct a few tutorials for the animators.)

7. Warning: Peter and Homer will show some skin. The episode hopes to clean up in laughs with a “sexy” car wash scene featuring a scantily clad Homer and Peter, set to Def Leppard’s “Pour Some Sugar on Me.” “The animators thought of very creative ways to use Peter and Homer’s combined 500 pounds pressed against car windshields that never left us without a literal explanation of what innocent body parts we were seeing,” says Appel.

8. Beer is the cause of—not the solution to—all of the problems between Peter and Homer. At the beginning of the episode, the two become fast friends. “When they find out what they each do, Peter says, ‘What’s a nuclear power plant?’ And Homer goes, ‘I don’t know.’ When Homer finds out that he works in a brewery, he says, ‘What’s beer really like?’ We explicitly have fun with some of the similarities between the two characters. They do both like beer, like a few other American men.” Alas, that leads to a major rift between the two. Hints Appel: “Homer discovers something that he thinks Pawtucket Pat has in common with Duff. And Mr. Burns’ lawyer was in Mo’s at the time and offers his assistance.”

9. How bad do things get between Peter and Homer? They have a nuclear chicken fight that lasts more than seven minutes. “This was fun for the animators in a different way because it was an entirely new town to destroy,” says Appel. “[The chicken fights] go all over the world but they start in Quahog, and this one starts in Springfield. So, right off the bat you think ‘All right, well, that’s a clean slate. What can we momentarily take down that they spent 25 years building?’” A highlight for the Family Guy team? Witnessing the recording session in which Castellaneta had to lay down all of Homer’s grunts, groans, and moans during the chicken fight. “One of the funniest things I’ve ever witnessed was the [seven] minutes of watching Dan watch the fight sequence on a monitor and ad-lib every sound effect that went with it,” says Appel. “It’s just a tribute to him that Homer’s sounds can make you laugh harder than most lines in any other TV show.”

10. The man that has been sandwiched in between The Simpsons and Family Guy on Sunday nights makes a drive-by, er, fly-by appearance. Yes, Bob Belcher (voiced by H. John Benjamin) from Bob’s Burgers has a brief cameo with Homer and Peter in a plane. (MacFarlane is a fan of Bob’s Burgers, as well as Home Movies, which, like Bob’s was created by Loren Bouchard and also features the vocal work of Benjamin.) The joke about Bob’s Burgers needing a protected time slot “was a line that gave the studio a little pause,” says Appel, “but I reminded them: We’re taking an even bigger shot at The Cleveland Show,” the Family Guy spin-off that Appel co-created.

11. Is there any chance of Homer & Co. paying a visit to Quahog in a future episode of The Simpsons? While The Simpsons’ Jean praises the episode and says that Family Guy “covered the territory really well,” he says there are currently no plans for that. He also notes that the Simpsons team is turning their attention to Nov. 9’s “Simpsorama,” in which the Planet Express crew from Futurama pay a visit to Springfield. And what about the possibility of a Family Guy sequel to “The Simpsons Guy”? “We say explicitly it’s a one-time only thing. But no one saw Archie Bunker’s Place coming either,” quips Appel. “So you never know.”